Thermally Driven Giant Bending of Liquid Crystal Elastomer Films with Hybrid Alignment

Abstract

We have investigated the thermally induced bending deformation of nematic elastomers with hybrid alignment (HNEs) where the director continuously rotates by 90 (from planar alignment to vertical alignment) between the top and bottom surfaces. The flat specimen of nematic gel in the preparation state exhibits a considerable bending when allowed to deswell to the dry state. The curvature of the dried elastomer film markedly depends on temperature. The curvature in the nematic state increases with heating, and the film apparently becomes flat at a certain temperature. Further heating induces the bending in the opposite direction. In the high-temperature isotropic state, the curvature is independent of temperature. This bending deformation is thermally reversible. We successfully interpret the temperature dependence of curvature for the HNEs assuming a linear variation of strain in the thickness direction on the basis of the thermally uniaxial deformation of the nematic elastomers with globally planar or vertical alignment. We also conduct a nume- rical simulation on the basis of a nonlinear elasticity model to reproduce the observation. The simulation using the material parameters that are almost identical with the corresponding experimental values explains the phenomenon and demonstrates the stress and strain distribution in the curled HNEs

Dimension reduction via $$\Gamma $$ Γ -convergence for soft active materials

“…Similar issues have been the object of recent intense investigation, see e.g. [3,6,22,23,27] and also [7,9,10,12,13,19,25]. The point of view we adopt here is that of a systematic derivation of dimensionally-reduced models by means of Γ-convergence.…”

Crawling on directional surfaces

“…Future work will consist in exploring the possibility of actually implement these concepts in practical designs exploiting active materials such as nematic elastomers [20,32], the effect of elastic instabilities [8,9,34], or bistable and hysteretic devices [15,19,24].…”

Shape control of active surfaces inspired by the movement of euglenids

“…by non-uniform swelling through the thickness, typically in quasi one-dimensional structures (Hu et al, 1995;Armon et al, 2011;Sawa et al, 2010;Urayama, 2012). In quasi two-dimensional structures, imposed bending alone, even if two-dimensional, provides access to a limited repertoire of shapes as it can only produce curvature in one direction due to the dominant stretching penalty of doubly curved shapes (Warner et al, 2010).…”

“…This viewpoint has been motivated by the shapes of flowers and leaves as a result of non-uniform growth (Nechaev and Voituriez, 2001;Marder and Papanicolaou, 2006;Sharon et al, 2004;Liang and Mahadevan, 2009;Amar et al, 2012), and has been implemented in disk and tubular topologies by non-uniform swelling/shrinkage of gels (Klein et al, 2007;Kim et al, 2012) or non-uniform switching of liquid crystal elastomers (deHaan et al, 2012;Sawa et al, 2010;Urayama, 2012). In these and most references, the non-uniformity in the deformation is accomplished by patterning non-uniform swelling or nematic director fields, see also e.g.…”